A good guild

You want to help people and a guild is the best way to do that. You'll still have to decide on a guild though.

"Fairy Tail" for example might be a good choice as they already have three Dragonslayers who could hep you further develop your powers. And while they might not be the most organised bunch the lack of rules that comes out of that might actually be a plus for you (from what you've heard they also have a lot of hot chicks you could have fun with!).

Another option would be "Blue Pegasus" another big guild and while their leader is a bit weird they certainly are caring as well as powerful.

You could also take a look at other guilds or research some smaller ones.